Regular messages are for onboarding purposes and are only sent once. Now that we are introducing a new type of message. I would call the new column on scheduled_messages type have it be an ActiveRecord enum that defaults to onboarding but can also be set to quarterly (like in the case for this feature)

Once quarterly is selected, the other fields that are specific to onboarding-type messages ( 'Business days after employee starts to send message' and 'Time of day to send message (uses employee's local time zone)') can either be hidden or disabled. whatever is easier.